Typically, vehicle bumper beams are required to pass legally mandated low-speed crash tests and quasi-legally mandated property insurance organization (ROAR, IIHS) tests. Here, the standards required by property insurance organizations are more stringent than those required by law, and depending on the region, both tests or only the legally mandated low-speed crash test is required. Thus, most finished vehicle manufacturers adopt high-strength bumper beams when required to satisfy property insurance organization-mandated tests, but adopt low-cost bumper beams in regions requiring only low speed crash tests mandated by law, thereby achieving vehicle price competitiveness.
Bumper beams designed to pass legally mandated low-speed crash tests are typically manufactured by injection molding, and thus, in terms of materials, various injection moldable materials may be used. However, it is necessary for bumper beams to exhibit the same performance satisfying low-speed crash performance requirements in various seasonal and use conditions, and so achieve dimensional stability such that there are no problems with respect to assembly and repairs. Accordingly, injection-molded bumper beams manufactured from PP-based materials and PC and PBT materials are typically used in regions with low seasonal and temperature variance.
However, applying materials such those described above to regions that experience both mild and low temperatures, or developing a single bumper beam that can be used in both temperate and low-temperature regions, is difficult, and thus vehicle manufacturers wanting to use a single bumper beam in various regions prefer glass fiber-containing composite plastic materials to those described above.
Composite plastic materials including glass fiber can be press-molded or injection-molded depending on fiber length, and longer glass fibers, although advantageous in terms of bumper beam strength, require press molding, which involves higher production costs than injection molding. Thus, since injection molding is advantageous with respect to lowering production costs but necessitates shorter glass fibers, injection-molded bumpers suffer more damage when subjected to legally mandated low-speed crash tests, and result in damage to the vehicle body. Thus, there is a limitation in that legal requirements cannot be satisfied. That is, currently, since it is necessary to adopt press molding in order to satisfy legal performance requirements for bumper beams using glass fiber-containing composite plastic materials, reducing productions costs is difficult.
In order to overcome such limitations, measures to strengthen the mechanical properties of polyolefin resin, which is a commonly used plastic that is easily molded, by mixing and stirring polyolefin resin with glass fiber have been continuously researched. However, in such methods, most of the glass fiber is significantly damaged inside roll-milling/mixing equipment, such that extremely short glass fibers are mixed with the polyolefin resin. Thus, strength improvement in products has been limited.
Therefore, there can be said to be a demand for developing a novel resin composition that is reinforced with glass fiber in the form of a long fiber and thus able to maintain a low specific gravity while exhibiting at least a desired level of mechanical properties, in particular, high impact strength.
For reference, see Korean Patent Nos. 10-0917651, 10-1457995 and 10-1365057, in which the background art for the present invention is disclosed.